That upgrade shouldn’t be offered at all until 26.04.1 is released in late August. Unless something has changed this is my understanding. I’ve not been offered it on on any of my Mate 24.04 machines.
That would be the proper thing to do in order not receive notifications to upgrade to the next LTS release. Regardless that upgrade shouldn’t be offered at all yet.
Here’s a thread that may be worth taking a look at though it would seem at the time it may only been happening to installs within a VM: